/* ----------------------------------------------------------------------
* Copyright (C) 2010 ARM Limited. All rights reserved.
*
* $Date:        15. February 2012
* $Revision: 	V1.1.0
*
* Project: 	    CMSIS DSP Library
* Title:	    arm_iir_lattice_f32.c
*
* Description:	Floating-point IIR Lattice filter processing function.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Version 1.1.0 2012/02/15
*    Updated with more optimizations, bug fixes and minor API changes.
*
* Version 1.0.10 2011/7/15
*    Big Endian support added and Merged M0 and M3/M4 Source code.
*
* Version 1.0.3 2010/11/29
*    Re-organized the CMSIS folders and updated documentation.
*
* Version 1.0.2 2010/11/11
*    Documentation updated.
*
* Version 1.0.1 2010/10/05
*    Production release and review comments incorporated.
*
* Version 1.0.0 2010/09/20
*    Production release and review comments incorporated
*
* Version 0.0.7  2010/06/10
*    Misra-C changes done
* -------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @ingroup groupFilters
 */

/**
 * @defgroup IIR_Lattice Infinite Impulse Response (IIR) Lattice Filters
 *
 * This set of functions implements lattice filters
 * for Q15, Q31 and floating-point data types.  Lattice filters are used in a
 * variety of adaptive filter applications.  The filter structure has feedforward and
 * feedback components and the net impulse response is infinite length.
 * The functions operate on blocks
 * of input and output data and each call to the function processes
 * <code>blockSize</code> samples through the filter.  <code>pSrc</code> and
 * <code>pDst</code> point to input and output arrays containing <code>blockSize</code> values.

 * \par Algorithm:
 * \image html IIRLattice.gif "Infinite Impulse Response Lattice filter"
 * <pre>
 *    fN(n)   =  x(n)
 *    fm-1(n) = fm(n) - km * gm-1(n-1)   for m = N, N-1, ...1
 *    gm(n)   = km * fm-1(n) + gm-1(n-1) for m = N, N-1, ...1
 *    y(n)    = vN * gN(n) + vN-1 * gN-1(n) + ...+ v0 * g0(n)
 * </pre>
 * \par
 * <code>pkCoeffs</code> points to array of reflection coefficients of size <code>numStages</code>.
 * Reflection coefficients are stored in time-reversed order.
 * \par
 * <pre>
 *    {kN, kN-1, ....k1}
 * </pre>
 * <code>pvCoeffs</code> points to the array of ladder coefficients of size <code>(numStages+1)</code>.
 * Ladder coefficients are stored in time-reversed order.
 * \par
 * <pre>
 *    {vN, vN-1, ...v0}
 * </pre>
 * <code>pState</code> points to a state array of size <code>numStages + blockSize</code>.
 * The state variables shown in the figure above (the g values) are stored in the <code>pState</code> array.
 * The state variables are updated after each block of data is processed; the coefficients are untouched.
 * \par Instance Structure
 * The coefficients and state variables for a filter are stored together in an instance data structure.
 * A separate instance structure must be defined for each filter.
 * Coefficient arrays may be shared among several instances while state variable arrays cannot be shared.
 * There are separate instance structure declarations for each of the 3 supported data types.
  *
 * \par Initialization Functions
 * There is also an associated initialization function for each data type.
 * The initialization function performs the following operations:
 * - Sets the values of the internal structure fields.
 * - Zeros out the values in the state buffer.
 *
 * \par
 * Use of the initialization function is optional.
 * However, if the initialization function is used, then the instance structure cannot be placed into a const data section.
 * To place an instance structure into a const data section, the instance structure must be manually initialized.
 * Set the values in the state buffer to zeros and then manually initialize the instance structure as follows:
 * <pre>
 *arm_iir_lattice_instance_f32 S = {numStages, pState, pkCoeffs, pvCoeffs};
 *arm_iir_lattice_instance_q31 S = {numStages, pState, pkCoeffs, pvCoeffs};
 *arm_iir_lattice_instance_q15 S = {numStages, pState, pkCoeffs, pvCoeffs};
 * </pre>
 * \par
 * where <code>numStages</code> is the number of stages in the filter; <code>pState</code> points to the state buffer array;
 * <code>pkCoeffs</code> points to array of the reflection coefficients; <code>pvCoeffs</code> points to the array of ladder coefficients.
 * \par Fixed-Point Behavior
 * Care must be taken when using the fixed-point versions of the IIR lattice filter functions.
 * In particular, the overflow and saturation behavior of the accumulator used in each function must be considered.
 * Refer to the function specific documentation below for usage guidelines.
 */

/**
 * @addtogroup IIR_Lattice
 * @{
 */

/**
 * @brief Processing function for the floating-point IIR lattice filter.
 * @param[in] *S points to an instance of the floating-point IIR lattice structure.
 * @param[in] *pSrc points to the block of input data.
 * @param[out] *pDst points to the block of output data.
 * @param[in] blockSize number of samples to process.
 * @return none.
 */

#ifndef ARM_MATH_CM0

/* Run the below code for Cortex-M4 and Cortex-M3 */

void arm_iir_lattice_f32(
    const arm_iir_lattice_instance_f32* S,
    float32_t* pSrc,
    float32_t* pDst,
    uint32_t blockSize)
{
	float32_t fnext1, gcurr1, gnext;               /* Temporary variables for lattice stages */
	float32_t acc;                                 /* Accumlator */
	uint32_t blkCnt, tapCnt;                       /* temporary variables for counts */
	float32_t* px1, *px2, *pk, *pv;                /* temporary pointers for state and coef */
	uint32_t numStages = S->numStages;             /* number of stages */
	float32_t* pState;                             /* State pointer */
	float32_t* pStateCurnt;                        /* State current pointer */
	float32_t k1, k2;
	float32_t v1, v2, v3, v4;
	float32_t gcurr2;
	float32_t fnext2;

	/* initialise loop count */
	blkCnt = blockSize;

	/* initialise state pointer */
	pState = &S->pState[0];

	/* Sample processing */
	while(blkCnt > 0u) {
		/* Read Sample from input buffer */
		/* fN(n) = x(n) */
		fnext2 = *pSrc++;

		/* Initialize Ladder coeff pointer */
		pv = &S->pvCoeffs[0];
		/* Initialize Reflection coeff pointer */
		pk = &S->pkCoeffs[0];

		/* Initialize state read pointer */
		px1 = pState;
		/* Initialize state write pointer */
		px2 = pState;

		/* Set accumulator to zero */
		acc = 0.0;

		/* Loop unrolling.  Process 4 taps at a time. */
		tapCnt = (numStages) >> 2;

		while(tapCnt > 0u) {
			/* Read gN-1(n-1) from state buffer */
			gcurr1 = *px1;

			/* read reflection coefficient kN */
			k1 = *pk;

			/* fN-1(n) = fN(n) - kN * gN-1(n-1) */
			fnext1 = fnext2 - (k1 * gcurr1);

			/* read ladder coefficient vN */
			v1 = *pv;

			/* read next reflection coefficient kN-1 */
			k2 = *(pk + 1u);

			/* Read gN-2(n-1) from state buffer */
			gcurr2 = *(px1 + 1u);

			/* read next ladder coefficient vN-1 */
			v2 = *(pv + 1u);

			/* fN-2(n) = fN-1(n) - kN-1 * gN-2(n-1) */
			fnext2 = fnext1 - (k2 * gcurr2);

			/* gN(n)   = kN * fN-1(n) + gN-1(n-1) */
			gnext = gcurr1 + (k1 * fnext1);

			/* read reflection coefficient kN-2 */
			k1 = *(pk + 2u);

			/* write gN(n) into state for next sample processing */
			*px2++ = gnext;

			/* Read gN-3(n-1) from state buffer */
			gcurr1 = *(px1 + 2u);

			/* y(n) += gN(n) * vN  */
			acc += (gnext * v1);

			/* fN-3(n) = fN-2(n) - kN-2 * gN-3(n-1) */
			fnext1 = fnext2 - (k1 * gcurr1);

			/* gN-1(n)   = kN-1 * fN-2(n) + gN-2(n-1) */
			gnext = gcurr2 + (k2 * fnext2);

			/* Read gN-4(n-1) from state buffer */
			gcurr2 = *(px1 + 3u);

			/* y(n) += gN-1(n) * vN-1  */
			acc += (gnext * v2);

			/* read reflection coefficient kN-3 */
			k2 = *(pk + 3u);

			/* write gN-1(n) into state for next sample processing */
			*px2++ = gnext;

			/* fN-4(n) = fN-3(n) - kN-3 * gN-4(n-1) */
			fnext2 = fnext1 - (k2 * gcurr2);

			/* gN-2(n) = kN-2 * fN-3(n) + gN-3(n-1) */
			gnext = gcurr1 + (k1 * fnext1);

			/* read ladder coefficient vN-2 */
			v3 = *(pv + 2u);

			/* y(n) += gN-2(n) * vN-2  */
			acc += (gnext * v3);

			/* write gN-2(n) into state for next sample processing */
			*px2++ = gnext;

			/* update pointer */
			pk += 4u;

			/* gN-3(n) = kN-3 * fN-4(n) + gN-4(n-1) */
			gnext = (fnext2 * k2) + gcurr2;

			/* read next ladder coefficient vN-3 */
			v4 = *(pv + 3u);

			/* y(n) += gN-4(n) * vN-4  */
			acc += (gnext * v4);

			/* write gN-3(n) into state for next sample processing */
			*px2++ = gnext;

			/* update pointers */
			px1 += 4u;
			pv += 4u;

			tapCnt--;

		}

		/* If the filter length is not a multiple of 4, compute the remaining filter taps */
		tapCnt = (numStages) % 0x4u;

		while(tapCnt > 0u) {
			gcurr1 = *px1++;
			/* Process sample for last taps */
			fnext1 = fnext2 - ((*pk) * gcurr1);
			gnext = (fnext1 * (*pk++)) + gcurr1;
			/* Output samples for last taps */
			acc += (gnext * (*pv++));
			*px2++ = gnext;
			fnext2 = fnext1;

			tapCnt--;

		}

		/* y(n) += g0(n) * v0 */
		acc += (fnext2 * (*pv));

		*px2++ = fnext2;

		/* write out into pDst */
		*pDst++ = acc;

		/* Advance the state pointer by 4 to process the next group of 4 samples */
		pState = pState + 1u;

		blkCnt--;

	}

	/* Processing is complete. Now copy last S->numStages samples to start of the buffer
	   for the preperation of next frame process */

	/* Points to the start of the state buffer */
	pStateCurnt = &S->pState[0];
	pState = &S->pState[blockSize];

	tapCnt = numStages >> 2u;

	/* copy data */
	while(tapCnt > 0u) {
		*pStateCurnt++ = *pState++;
		*pStateCurnt++ = *pState++;
		*pStateCurnt++ = *pState++;
		*pStateCurnt++ = *pState++;

		/* Decrement the loop counter */
		tapCnt--;

	}

	/* Calculate remaining number of copies */
	tapCnt = (numStages) % 0x4u;

	/* Copy the remaining q31_t data */
	while(tapCnt > 0u) {
		*pStateCurnt++ = *pState++;

		/* Decrement the loop counter */
		tapCnt--;
	}
}

#else

void arm_iir_lattice_f32(
    const arm_iir_lattice_instance_f32* S,
    float32_t* pSrc,
    float32_t* pDst,
    uint32_t blockSize)
{
	float32_t fcurr, fnext = 0, gcurr, gnext;      /* Temporary variables for lattice stages */
	float32_t acc;                                 /* Accumlator */
	uint32_t blkCnt, tapCnt;                       /* temporary variables for counts */
	float32_t* px1, *px2, *pk, *pv;                /* temporary pointers for state and coef */
	uint32_t numStages = S->numStages;             /* number of stages */
	float32_t* pState;                             /* State pointer */
	float32_t* pStateCurnt;                        /* State current pointer */


	/* Run the below code for Cortex-M0 */

	blkCnt = blockSize;

	pState = &S->pState[0];

	/* Sample processing */
	while(blkCnt > 0u) {
		/* Read Sample from input buffer */
		/* fN(n) = x(n) */
		fcurr = *pSrc++;

		/* Initialize state read pointer */
		px1 = pState;
		/* Initialize state write pointer */
		px2 = pState;
		/* Set accumulator to zero */
		acc = 0.0f;
		/* Initialize Ladder coeff pointer */
		pv = &S->pvCoeffs[0];
		/* Initialize Reflection coeff pointer */
		pk = &S->pkCoeffs[0];


		/* Process sample for numStages */
		tapCnt = numStages;

		while(tapCnt > 0u) {
			gcurr = *px1++;
			/* Process sample for last taps */
			fnext = fcurr - ((*pk) * gcurr);
			gnext = (fnext * (*pk++)) + gcurr;

			/* Output samples for last taps */
			acc += (gnext * (*pv++));
			*px2++ = gnext;
			fcurr = fnext;

			/* Decrementing loop counter */
			tapCnt--;

		}

		/* y(n) += g0(n) * v0 */
		acc += (fnext * (*pv));

		*px2++ = fnext;

		/* write out into pDst */
		*pDst++ = acc;

		/* Advance the state pointer by 1 to process the next group of samples */
		pState = pState + 1u;
		blkCnt--;

	}

	/* Processing is complete. Now copy last S->numStages samples to start of the buffer
	   for the preperation of next frame process */

	/* Points to the start of the state buffer */
	pStateCurnt = &S->pState[0];
	pState = &S->pState[blockSize];

	tapCnt = numStages;

	/* Copy the data */
	while(tapCnt > 0u) {
		*pStateCurnt++ = *pState++;

		/* Decrement the loop counter */
		tapCnt--;
	}

}

#endif /*   #ifndef ARM_MATH_CM0 */


/**
 * @} end of IIR_Lattice group
 */
